Promoting Water Activation by Photogenerated Holes in Monolayer C₂N

In photocatalytic reactions, the activation of H₂O is very important for achieving high energy conversion efficiency. However, its activation mechanism under photoirradiation is still not fully understood. Here, on the basis of first-principles calculations, the role of photogenerated holes on the activation of H₂O is investigated in a typical photocatalytic material C₂N. The H₂O molecule adsorbs at the six-membered N pore of C₂N with a dual H-bonding configuration. Due to the electrostatic repulsion between the O atom of H₂O and six N atoms of C₂N, the energy level of the H₂O molecule's highest occupied molecular orbital is raised significantly to exceed the valence band maximum of C₂N, so that the photogenerated holes in C₂N can be quickly captured by the H₂O molecule. The captured photogenerated holes boost the activation of H₂O and reduce the dissociation energy barrier from 1.61 to 0.69 eV. Besides, p-type defects of C₂N have similar effects as photogenerated holes.